This invention relates generally to shaft driven bicycles and, more particularly, to a multi-speed inline bicycle transmission having simple and compact gearing for improved torque transfer and durability.
Typical multi-speed bicycles utilize a derailleur gear chain assembly which includes multiple sprockets of different diameters onto which a bicycle chain is selectively routed in order to change transmission ratios. Chain driven transmissions, however, include several disadvantages, such as a chain slipping off a sprocket, tensioner mechanism malfunction, clothing becoming entangled in the chain, dirt or debris build-up in chain linkages, etc.
Various chainless transmissions for bicycles have been proposed in the art for overcoming the above-mentioned disadvantages. Although assumably effective for their intended purposes, the existing chainless transmissions utilize friction roller designs that are not durable and allow power losses greater than any gains in efficiency or require multiple moving parts for changing gear ratios.
Therefore, it would be desirable to have an inline bicycle transmission for selectively modifying the transmission ratio of a drive shaft rotational force mounted inline relative to a drive shaft and which efficiently transfers that force to a bicycle rear wheel. Further, it would be desirable to have an inline bicycle transmission which selectively transmits torque between input and output drive shaft portions using highly efficient and durable straight cut gears and without power losses associated with transmitting power between angled shafts.
A multi-speed inline bicycle transmission according to the present invention includes a drive shaft having input and output portions. An upstream end of the input portion is connected to the crank axle of a bicycle crank-and-pedal assembly with a pair of bevel gears for efficiently transmitting a rotational force from the crank axle to the drive shaft input portion. An epicyclic gear train encased in a gear box is mounted inline to the drive shaft intermediate drive shaft input and output portions. The epicyclic gear train includes a plurality of compact, straight cut gears for establishing predetermined transmission ratios. Thus, a rotational force of the drive shaft input portion may be transmitted to the drive shaft output portion in an inline configuration without the inefficiencies or power loss experienced by more complex gear configurations or constructions. Further, the epicyclic gear train may provide multiple gear ratio selections without significantly increasing the size or complexity of the gear train. The epicyclic gear train is connected to the output portion where the output rotational force is efficiently transmitted to the bicycle rear wheel axle through another pair of bevel gears.
Therefore, a general object of this invention is to provide a multi-speed inline shaft-driven transmission for a bicycle that is compact, durable, and efficient.
Another object of this invention is to provide a bicycle transmission, as aforesaid, which utilizes two sets of bevel gears for efficiently transferring power between angled shafts.
Still another object of this invention is to provide a bicycle transmission, as aforesaid, which provides multiple gear ratios without using any clutches.
Yet another object of this invention is to provide a bicycle transmission, as aforesaid, which utilizes straight cut gears to provide variable transmission ratios.